E-guns are used for various applications and particularly for vapor deposition processes. Such deposition systems typically include an electron emitting source, a crucible for holding the evaporant, and means for directing the electron beam onto the surface of the evaporant. U.S. Pat. Nos. 3,710,072 and 5,111,022 show various details of prior art E-guns.
Multi-pocket E-guns provide a plurality of pockets in a crucible whereby the crucible can be rotated to place a different one of the pockets in the position at which the electron beam is focused. A multi-pocket E-gun is described in U.S. Pat. No. 4,983,806. Typically an E-gun crucible is liquid cooled, such as with water, and in the rotatable crucible E-guns the water is conveyed to the crucible through lines which include a rotatable seal at the air/vacuum interface. These vacuum seals often use O-ring seals which cause outgassing and/or low level vacuum leaks which present serious problems when very high level vacuum deposition processes are used such as in molecular beam epitaxial processing where the vacuum may be on the order of 1.times.10.sup.-11 to 1.times.10.sup.-12 mm of Hg.
One present attempt to provide the appropriate high vacuum seal is to provide metallic, liquid inlet and outlet tubes to the crucible with the tubes aligned parallel to the rotational axis of the crucible and with a flexible portion, such as a bellows, along the length of the tube so that as the crucible is rotated to place the different pockets in desired position the liquid tubes can rotate around the rotational axis and twist along their length at the bellows. This structure results in extensive stress to the bellows when the liquid lines are twisted and increases the possibility of a failure in the bellows which can bring the system up to atmosphere and more importantly, dump liquid coolant into the vacuum chamber.
The object of the present invention is to provide a liquid cooling system for E-guns which insures maintenance of a high vacuum seal while permitting rotation of the liquid cooled rotatable crucible structure of the E-gun assembly.